1. Field of the Invention
The present invention relates to a recordable optical disc, and more particularly to a recordable optical disc suitable for recording signal according to CDV (Compact Disc Video) format.
2. Description of the Prior Art
Conventionally, there is CD (Compact Disc), known as a media for reproduction only, on which music information is recorded. There has recently been developed a recordable compact disc (CD-R:Recordable Compact Disc). Recording format of CD-R is generally referred to as "Orange Book", and it is in conformity with recording format of CD. FIGS. 1A and 1B illustrate physical format of CD-R. In CD-R, a lead-in area 4, a program area 5 and a lead-out area 6 are formed from inner circumference of the disc to outer circumference thereof, like the format of CD. In addition, in CD-R, a PCA (Power Calibration Area) 2 and a PMA (Power Memory Area) 3 are provided radially inwardly of the lead-in area 4, as illustrated.
Recording track on the R-CD is provided with guide groove that is wobbled by the frequency of a carrier of 22.05 kHz which is frequency-modulated by data indicating absolute time information (ATIP: Absolute Time In Pregroove). A laser beam for recording desired information is moved to follow the guide grooves under tracking servo control, and rotational speed of spindle motor which rotates the R-CD is controlled so that the wobbling guide groove pattern has a central frequency of 22.05 kHz. In this manner, tracking servo and spindle-motor servo controls can be effected on unrecorded R-CDs as well as recorded R-CDs.
The PCA 2 is an area where test recording is carried out prior to an actual information recording process, so that the power of the recording laser beam will be optimized for recording desired information in the information recording process. The PCA 2 is composed of a count area and a test area. The count area has a plurality of subareas corresponding respectively to a plurality of subareas of the test area, and each containing a suitable EFM signal recorded therein. Test recording for measuring an optimum recording laser beam power is carried out in the subareas of the test area. One of the subareas of the test area is consumed by a single test recording.
Any subarea of the test area which has once been used by test recording is not available for a next test recording. It is therefore necessary to search for an unused subarea positioned radially inwardly of the used subarea for use in the next test recording. The count area is provided to facilitate the searching process. More specifically, if suitable EFM signals have been recorded in certain subareas of the count area and no EFM signal has been recorded in a subarea next to those subareas, then unrecorded subarea indicates that the corresponding subarea of the test area is available for test recording. Consequently, that corresponding subarea of the test area may be searched for and test recording carried out therein for measuring an optimum recording laser beam power. After an optimum recording laser beam power has been measured in the subarea of the test area, the corresponding subarea of the count area is searched for, and a certain signal (EFM signal) is recorded in that subarea, indicating that test recording has already been conducted in the subarea of the count area.
The PMA 3 is an area for storing a recording history of information successively recorded in the program area. Specifically, start addresses and end addresses of track numbers recorded in the program area, for example, are recorded in the PMA 3 in the same format as the TOC information in the lead-in area.
The recording history of successively recorded information is stored in the PMA 3 for the following reasons: On a partially recorded disc, information may further be recorded in the remaining blank of the program area. Therefore, the information in the PMA 3 cannot be recorded in the lead-in area 4 until the completion of recording of all the desired information is finally indicated. Consequently, information about the tracks that have already been recorded is temporarily stored in the PMA 3. When the user or controller of the disc indicates that no more information will be recorded, the TOC information and a lead-out signal are recorded for the first time. At the time the recording is completed, the TOC information in the PMA 3 is transferred to the lead-in area 4 a plurality of times for improving reliability. The finalized disc (CD-R), on which the recording of all the necessary information is completed, is now in conformity with the CD format, and can be played back by an ordinary playback-only disc player which does not have an ATIP decoder for decoding the ATIP information. Not only the above-mentioned "Orange Book" but Japanese Patent Applications Nos. 3-23595 and 3-193218 disclose details of recording format of CD-R.
On the other hand, there is CDV (Compact Disc Video), known as application media of CD, which utilizes format of CD and LD (Laser Disc) in combination so as to record both audio and video signals on a unique disc. FIGS. 2A and 2B illustrate basic format of CDV. The CDV roughly includes an audio signal recording area positioned at inner circumferential portion of the disc for recording digital audio information and a video signal recording area positioned at outer circumferential portion of the disc for recording digital audio information and video information. The audio signal recording area includes a first lead-in area 11, a first program area 12 and a first lead-out area 13, and digital audio information for approximately 20 minutes is recorded according to the same format as CD. The video signal recording area includes a second lead-in area 14, a second program area 15 and a second lead-out area 16, and video information and digital audio information for approximately 5 minutes is recorded according to the same format as LD.
However, when CDV-format signal is actually recorded on the CD-R, a problem in respect to wobble frequency takes place due to difference of linear velocity of disc rotation between the audio signal recording area and the video signal recording area. When CD-R is divided into a first area (audio recording area) and a second area (video recording area) and signal according to CDV-format is to be recorded, a CLV servo is controlled at wobble frequency 22.05 kHz in the first area because the disc is rotated in the first area at linear velocity 1.2-1.4 m/s. However, in the second area according to CDV-format, linear velocity of disc rotation ranges 11-12 m/s, approximately 8 times of that in the first area, because frequency band width of video signal to be recorded is broad. Therefore, when a multiplexed signal of frequency-modulated video signal and a predetermined digital signal (EFM signal) is to be recorded in the second area at linear velocity 11.4 m/s, the wobble frequency f is required to be: EQU f=22.05.times.11.4/1.4=180 kHz.
This means that the signal to be recorded interferes with the frequency band of EFM signal (196-720 kHz), and therefore it is impossible to record digital signal in the second area.